Skeletal myoblasts offer an easily expandable source of autologous myogenic cells for cardiac repair. Despite their remarkable potential and the encouraging results emanating from their use in animal studies and human phase-1 trials, there are fundamental issues confronting the development of this approach to achieve better prognosis. This includes optimization of transplantation conditions, the immunobiology and mechanism of donor cell survival after transplantation, the underlying mechanism of their contribution towards improved cardiac function and effectiveness of combo-therapy involving myoblast transplantation with multiple angiogenic gene delivery using non-viral vector transfection. Our fundamental hypothesis is that primary skeletal myoblasts are conditionally immunoprivileged when transplanted across the histocompatibility barriers. Clonal selection of sub-populations of primary myoblasts may help to identify their immunological behavior. The fusion competent donor myoblast having a complete set of normally functioning genes, undergo fusion with the ischemically damaged host cardiomyocytes, compensate for their lost genes and form mosaic muscle fibers which contribute towards the improved cardiac performance. Moreover, angiogenic synergy through multiple angiogenic growth factor genes administration, together with myoblast transplantation may help to enhance the survival of donor skeletal myoblasts together with angiomyogenesis for cardiac repair. These hypotheses will be tested in well-established rat and porcine heart models of myocardial infarction, using a multidisciplinary approach including physiology, biochemistry, molecular biology, immunohistochemistry, and gene therapy. The specific aims of our proposal are: Aim-1) to characterize in vitro and define the in vivo behavior of human skeletal myoblast post transplantation in an animal model of myocardial infarction and develop strategies to elucidate the mechanism of the donor myoblast survival and define the immunologic basis of myoblast transplantation for cardiac repair. The results of these studies will pave the way for the use of myoblast from allogenic source and overcome the logistic problems associated with the use of autologous myoblast. Aim-2 to study the exact mechanism of improvement in the cardiac function after myoblast transplantation therapy. Aim-3 to define and optimize the transplantation conditions with respect to cell number, number of sites to be injected, optimum time for cell transplantation after the onset of infarction episode, and the preferential route of administration to achieve optimum prognosis. Aim-4 to transfect skeletal myoblasts with multiple angiogenic growth factor genes to achieve angiogenic synergy between various growth factors and myoblast therapy for cardiac repair. We believe that the findings of this proposal may eventually lead to achieve better prognosis from skeletal myoblast transplantation in the clinical perspective.